A number of techniques are known for the removal of impurities (either singular impurities or combined impurities) from inert gas, among these are the following.
A first method utilizes metal "getters", typically composed of mixtures of zirconium, aluminum, iron and vanadium, to remove impurities from an inert gas by reaction or chemisorption. A major disadvantage of this method is the necessity for operation at high temperature (400.degree. C.) with even higher temperatures for initial activation (500.degree.-700.degree. C.). Additionally, these materials have a limited capacity and can only be regenerated and reused a small number of times before their effectiveness is lost.
A second method utilizes a platinum group catalyst (e.g., platinum and palladium) to remove oxygen from an inert gas by reaction with added hydrogen at temperatures from ambient to 300.degree. C.; this second method is described in U.S. Pat. No. 3,535,074. In this particular description, a second absorber bed utilizing copper or nickel is used to remove any transient high concentrations of oxygen. The added hydrogen is removed by distillation of the product.
A third method utilizes reduced copper or nickel containing beds at temperatures from ambient to 250.degree. C. for removal of oxygen. These beds are regenerated from the oxidized state by reduction with a stream containing hydrogen.
Two methods have been described in the art for the removal of combined impurities of oxygen, hydrogen, carbon monoxide, carbon dioxide and hydrogen.
The first of these two methods is described in U.S. Pat. No. 4,579,723, wherein a commercial catalyst material (e.g., Engelhard Deoxo A containing Cr and Pt) is used to react carbon monoxide and hydrogen with oxygen at ambient temperature forming carbon dioxide and water. Residual oxygen and carbon dioxide are removed in a second bed containing a gettering material (e.g., Dow Q1) which is effective to remove oxygen and carbon dioxide. Water is removed by adsorption in one or both beds. It is necessary to regenerate the beds with a hydrogen containing stream at about 200.degree. C. to maintain their effectiveness.
In the second of these methods a nickel containing bed is used to simultaneously remove oxygen, carbon monoxide, hydrogen, water and carbon dioxide from an inert gas at ambient temperature; this method is disclosed in U.S. Pat. No. 4,713,224. The nickel containing bed is subsequently regenerated with a hydrogen containing stream.
In all of these above processes, it is necessary that the hydrogen be added to the process either for the primary removal of the impurity or for regeneration. This addition of hydrogen adds the cost of the hydrogen supply and the provision of equipment to ensure the safe handling of hydrogen.
Other processes known in the art are disclosed in U.S. Pat. Nos. 3,061,403; 3,682,585 and 4,459,270 and Australian Pat. No. 16826/53.